When the trigger is pulled, the piston, accompanied by the breech block, is propelled forward by the recoil spring; the breech block pushes a cartridge from the feed strip into the chamber; the cams on the upper face of the piston act on the fermeture nut, locking the breech; the firing pin is driven against the primer and the shot fired.
When the bullet in its passage through the bore has passed the port leading to the gas nozzle, a small portion of the powder gas, conducted by the port and the gas nozzle, impinges in the cup-shaped forward extremity of the piston, and drives it to the rear. As already explained, the breech is now unlocked by the action of the piston cams on the fermeture nut, the breech block is withdrawn, along with the extractor holding the spent cartridge case, which later is ejected when its head strikes the ejector.
Towards the end of the backward stroke of the piston a cam on its side imparts a slight rotary movement to the feed piece, which advances the feed strip sufficiently to bring the following cartridge to the loading position.
The last cartridge having been fired, the strip is ejected from the gun. Under the action of its spring, the feed piece, which has been held up by the strip, now descends, and, engaging with the shoulder of the piston, locks the breech open. All is now ready for the introduction of another strip.
The firing gear may be set for continuous firing, single shots, or safety, by turning the cocking handle to the positions marked “A,” “R” and “S,” respectively.
When set at “A” (automatic), so long as the trigger is held back, the piston is free to move forward again under the action of the recoil spring. As a result the gun fires continuously until the strip is exhausted or the trigger released.
When set at “R” (repetition), a separate pull of the trigger is required for each shot, as the sear engages with the piston each time the latter recoils, thus stopping the firing.
When set at “S” (safety) the trigger is locked, and cannot be pulled back. As a result the gun cannot be fired.
TO STRIP AND ASSEMBLE THE GUN.
1st.—Close breech.